Method of forming self-aligned thin capacitively-coupled thyristor structure

ABSTRACT

A semiconductor memory device having a thyristor is manufactured in a manner that makes possible self-alignment of one or more portions of the thyristor. According to an example embodiment of the present invention, a gate is formed over a first portion of doped substrate. The gate is used to mask a portion of the doped substrate and a second portion of the substrate is doped before or after a spacer is formed. After the second portion of the substrate is doped, the spacer is then formed adjacent to the gate and used to mask the second portion of the substrate while a third portion of the substrate is doped. The gate and spacer are thus used to form self-aligned doped portions of the substrate, wherein the first and second portions form base regions and the third portion form an emitter region of a thyristor. In another implementation, the spacer is also adapted to prevent formation of salicide on the portion of the thyristor beneath the spacer, self-aligning the salicide to the junction between the second and third portions. In addition, dimensions such as width and other characteristics of the doped portions that are used to form a thyristor can be controlled without necessarily using a separate mask.

FIELD OF THE INVENTION

The present invention is directed to semiconductor devices and, more specifically, to semiconductor devices including thyristor-based devices.

BACKGROUND

Recent technological advances in the semiconductor industry have permitted dramatic increases in integrated circuit density and complexity, and equally dramatic decreases in power consumption and package sizes. Presently, single-die microprocessors are being manufactured with many millions of transistors, operating at speeds of hundreds of millions of instructions per second and being packaged in relatively small, air-cooled semiconductor device packages. The improvements in such devices have led to a dramatic increase in their use in a variety of applications. As the use of these devices has become more prevalent, the demand for reliable and affordable semiconductor devices has also increased. Accordingly, the need to manufacture such devices in an efficient and reliable manner has become increasingly important.

An important part in the circuit design, construction, and manufacture of semiconductor devices concerns semiconductor memories and other circuitry used to store information. Conventional random access memory devices include a variety of circuits, such as SRAM and DRAM circuits. The construction and formation of such memory circuitry typically involves forming at least one storage element and circuitry designed to access the stored information.

There are a number of semiconductor memories in widespread use. Two such semiconductor memories are SRAM and DRAM. DRAM is very common due to its high density (e.g., high density has benefits including low price). DRAM cell size is typically between 6 F² and 8 F², where F is the minimum feature size. However, with typical DRAM access times being about 50 nSec, DRAM is relatively slow compared to typical microprocessor speeds and requires refresh. SRAM is another common semiconductor memory that is much faster than DRAM and, in some instances, is an order of magnitude faster than DRAM. Also, unlike DRAM, SRAM does not require refresh. SRAM cells are typically made using 4 transistors and 2 resistors or 6 transistors, which result in much lower density and is typically between about 60 F² and 100 F².

Various SRAM cell designs based on NDR (Negative Differential Resistance) constructions have been introduced, ranging from a simple bipolar transistor to complicated quantum-effect devices. These cell designs usually consist of at least two active elements, including an NDR device. In view of size considerations, the construction of the NDR device is important to the overall performance of this type of SRAM cell. One advantage of the NDR-based cell is the potential of having a cell area smaller than four-transistor and six-transistor SRAM cells because of the smaller number of active devices and interconnections.

Conventional NDR-based SRAM cells, however, have many problems that have prohibited their use in commercial SRAM products. These problems include, among others: high standby power consumption due to the large current needed in one or both of the stable states of the cell; excessively high or excessively low voltage levels needed for the cell operation; stable states that are too sensitive to manufacturing variations and provide poor noise-margins; limitations in access speed due to slow switching from one state to the other; limitations in operability due to temperature, noise, voltage and/or light stability; and manufacturability and yield issues due to complicated fabrication processing.

A thin capacitively-coupled thyristor-type NDR device can be effective in overcoming many previously unresolved problems for memory applications. An important consideration in the design of the thin capacitively-coupled thyristor involves designing the body of the thyristor sufficiently thin, so that the capacitive coupling between the control port and the thyristor base region can substantially modulate the potential of the base region. For memory-cell applications, another important consideration in semiconductor device design, including those employing thin capacitively-coupled thyristor-type devices, includes forming devices in a very dense array.

NDR devices including thyristors are also widely used in power switching applications because the current densities carried by such devices can be very high in their on state. In typical power applications, high voltages force thyristor devices to be very large. In some cases, the entire wafer is used to make one thyristor (e.g., no logic devices are combined with the thyristor). The performance of such NDR devices is dependent on many physical parameters, including the length of various regions of the thyristor. One manner for forming regions to a selected length includes using a masking technique such as photolithography. On very large thyristors, diffusion and/or epitaxial grown layer(s) may also be used. However, variation in the photolithographic process provided by currently-available photolithography techniques can hinder the ability to make one or more of the regions to a desired length and/or width, which can cause problems in some applications.

In high-density memory applications where high temperature diffusion steps can degrade logic devices and where photolithography is being used to produce the smallest features possible, traditional techniques used for fabricating thyristors, including those discussed above, do not work well. Specifically, additional length may be necessary for misalignment and process variation, which makes the device larger. The larger device may be acceptable for power thyristors, but not necessarily for devices such as high density memory cells. In addition, if a salicide block is also needed to prevent a salicide short between the regions of the thyristor, the length of the region being defined can be even longer (e.g., if the salicide block is also defined by photolithography, requiring additional space for misalignment). In a memory cell having mirrored thin capacitively-coupled thyristor elements, width variation aggravates the performance of the cell because misalignment can cause adjacent cells to have regions of different widths.

These and other design considerations have presented challenges to efforts to implement such a thin capacitively-coupled thyristor in bulk substrate applications, and in particular to highly dense applications.

SUMMARY

The present invention is directed to the manufacture of a thyristor in a manner that addresses the above-mentioned challenges. The present invention is exemplified in a number of implementations and applications, some of which are summarized below.

According to an example embodiment of the present invention, a gate and a spacer are used to mask portions of a semiconductor substrate for implanting the substrate with a dopant for forming a thyristor. A portion of the substrate is doped, and a thyristor gate is formed over a first region of the doped substrate. The gate is used to mask the first region and a second region of the substrate is doped. A sidewall spacer is formed adjacent to the gate over the second region and used to mask the second region while a third region of the substrate is doped. In the resulting structure, the first and third regions are each contiguously adjacent to the second region. The thyristor includes doped regions of which the first and second regions are base regions and the third region is an emitter region of the thyristor. The dimension of the second doped thyristor region is controlled using a spacer for self-alignment. If left in place, the sidewall spacer also acts to block the formation of self-aligned silicide (salicide) on the surface of the second doped thyristor region. In this manner, the alignment and definition of the second doped portion is facilitated.

In a related embodiment, a thyristor includes a capacitively-coupled control port and an underlying thyristor-body region being aligned so that the control port does not extend beyond one or both of the junction-defining edges.

The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and detailed description that follow more particularly exemplify these embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in consideration of the detailed description of various embodiments of the invention in connection with the accompanying drawings, in which:

FIG. 1A shows a thyristor device at a relatively early stage of manufacture, according to an example embodiment of the present invention;

FIG. 1B shows the thyristor device of FIG. 1A after further manufacture, according to another example embodiment of the present invention;

FIG. 1C shows the thyristor device of FIG. 1B after further manufacture, according to another example embodiment of the present invention;

FIG. 1D shows the thyristor device of FIG. 1C after yet further manufacture, according to another example embodiment of the present invention;

FIG. 1E shows a thyristor device undergoing manufacture, according to another example embodiment of the present invention.

FIG. 2 shows a thyristor device manufactured in accordance with another example embodiment of the present invention;

FIG. 3 shows a thyristor device manufactured in accordance with another example embodiment of the present invention;

FIG. 4A shows another thyristor device at a relatively early stage of manufacture, according to another example embodiment of the present invention;

FIG. 4B shows the thyristor device of FIG. 4A after further manufacture, according to another example embodiment of the present invention;

FIG. 4C shows the thyristor device of FIG. 4B after further manufacture, according to another example embodiment of the present invention;

FIG. 5A shows a thyristor device at a relatively early stage of manufacture, according to yet another example embodiment of the present invention;

FIG. 5B shows the thyristor device of FIG. 5A after further manufacture, according to another example embodiment of the present invention;

FIG. 5C shows the thyristor device of FIG. 5B after further manufacture, according to another example embodiment of the present invention;

FIG. 5D shows the thyristor device of FIG. 5C after further manufacture, according to another example embodiment of the present invention;

FIG. 6A shows another thyristor device at an early stage of manufacture, according to another example embodiment of the present invention;

FIG. 6B shows the thyristor device of FIG. 6A after further manufacture, according to another example embodiment of the present invention;

FIG. 6C shows the thyristor device of FIG. 6B after further manufacture, according to another example embodiment of the present invention;

FIG. 7A shows another thyristor device at an early stage of manufacture, according to another example embodiment of the present invention; and

FIG. 7B shows the thyristor device of FIG. 6A after further manufacture, according to another example embodiment of the present invention.

While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not necessarily to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION

The present invention is believed to be applicable to a variety of different types of semiconductor devices, and has been found to be particularly suited for SOI (Silicon-on insulator) devices using thyristor-based devices, such as memory cells, and for enhancing the ability to form such devices. While the present invention is not necessarily limited to such devices, various aspects of the invention may be appreciated through a discussion of various examples using this context.

According to an example embodiment of the present invention, a thyristor is formed in a substrate using a control port and a spacer adjacent to the control port to mask one or more portions of the substrate for implantation. The implantation masked by the spacer results in a thyristor base region that is self-aligned to the control port and spacer edges, with the thyristor base region having a dimension defined as a function of the width of the spacer. In this manner, variation in the dimensions of the base that can occur using conventional formation methods, such as using a photolithographically defined layer to mask implantation of the thyristor base region, are reduced. The reduction in variation allows the formation of thyristor base regions that exhibit dimensions closer to design dimensions.

The approach discussed above is also useful, for example, in manufacturing mirrored thyristor devices having base regions with consistently smaller relative dimensions than can be manufactured using a photoresist mask during implantation for defining the dimensions. In addition, forming a thyristor in this manner is useful in high density applications, such as in memory applications where the thyristor is adapted for storing information.

In another example embodiment of the present invention, a spacer formation process used in forming a CMOS logic gate is used to form a thyristor as well. For example, the base region of a thyristor can be self-aligned to the CMOS logic spacer, as discussed above. The spacer size used in the CMOS logic gate is selected to meet specifications for the thyristor such that no adjustment in spacer size is required for self-aligning a region of the thyristor. In this instance, a control port is formed over a first base region of the thyristor, a second base region is implanted adjacent to the first base region below the control port, and a spacer is formed on the sidewall of the control port. The spacer has a width extending over the second base region and selected for defining a width of the second base region. An emitter region is formed self-aligned to the edge of the sidewall spacer.

FIGS. 1A through 1D show a thin capacitively coupled thyristor being manufactured, according to a more particular example embodiment of the present invention. In FIG. 1A, a gate structure 110 (e.g., a control port structure) is formed over a substrate 102 having a region 105 of P doping to be used to form a P-base region. The gate structure includes a gate dielectric 116 formed on an upper surface 104 of the substrate and polysilicon 118 formed on the dielectric. In FIG. 1B, a mask 122 (e.g., a photoresist) is formed over a portion of the gate structure 110 and of the upper surface 104 of the substrate 102. Using the mask 122 and the gate structure 110 to mask the substrate, an N-base region 140 is implanted adjacent to the P-base region 105, forming a p-n junction region 142. As discussed in connection with FIG. 3, the N-base region can be offset from the corner of the gate structure 110.

In FIG. 1C, the mask 122 is removed, spacers 112 and 114 are formed adjacent to the gate polysilicon 118 and dielectric 116, and a mask 132 is formed over the spacer 112 and over a portion of each of the upper surface 104 of the substrate 102 and the gate structure 110. A P+ implant is effected to form P+ region 150, using the spacer 114 to mask a portion of the N-base region 140. P+ region 150 and N-base region 140 form an anode end portion of the thyristor having a p-n junction 144 that, together with p-n junction 142, defines a width of the N-base region 140. In this manner, the N-base region 140, as defined by p-n junction 144, is self-aligned to the spacer 114.

Referring now to FIG. 1D, the mask 132 is removed after the P+ region is implanted and a mask 134 (e.g., a photoresist) is formed over the P+ region 150, the spacer 114 and the polysilicon gate 118. An N+ implant is effected to form N+ emitter region 130 that is adjacent to the P-base region 105. The N+ emitter region and the P-base regions form a p-n junction 146 and define a cathode end portion of the thyristor. The resulting thyristor has a body defined by the cathode end portion that includes the N+ emitter region 130 and the P-base region 105 and by the anode end portion that includes the N-base region 140 and P+ emitter region 150. The gate polysilicon 118 is capacitively coupled via the gate dielectric 116 to the P-base region 105 and forms a control gate for the thyristor.

In another example embodiment of the present invention, the size of the spacer used in a CMOS logic gate process is adjusted (e.g., increased) to selectively change the spacer size to meet specifications for use in forming a self-aligned portion of a thyristor. In one particular implementation, a thyristor is formed as shown in FIGS. 1A and 1B and as described above, wherein the thin capacitively-coupled thyristor undergoes further manufacturing as shown in FIG. 1E after the N-base region 141 is implanted. Spacers 112 and 114 are formed adjacent the polysilicon gate 118 and the gate dielectric 116. A layer of the spacer material is deposited and etched back (not shown) to form an additional spacer 152. The resulting spacer 152 is formed over a portion of the polysilicon 118, sidewall 114 and the upper surface 104. A mask 124 is then formed over a portion of the gate polysilicon 118, the spacer 112 and the N+ emitter region 130. A P+ implant is effected to form P+ region 151 using the spacer 152 and the mask 124 to mask a portion of the substrate such that the implant below these regions is inhibited. A portion 153 of the spacer layer that is formed on the upper surface 104 of the substrate is adapted to only partially inhibit the P+ implant, resulting in dopant passing through the spacer layer 153 and forming a laterally-extended portion 145 of the N-base. The thickness of the spacer layer portion 153 is selected for controlling the depth of the implant, depending upon the application. For example, a thicker spacer layer further inhibits the P+ doping and a thinner spacer layer allows more dopant to pass into the substrate. In other particular example embodiments, the various spacers are used to form the P-base region junctions at or to the outside of both edges of the overlying control port.

The resulting P+ emitter region below the spacer layer 153 is shallower than the P+ emitter region below the upper surface 104 not having spacer layer formed thereon. A p-n junction 146 between the P+ emitter region 151 and the N-base region 141, together with the p-n junction 142, define a width characteristic of the N-base region using the gate and spacer 152 for self-alignment. The N-base region 141 and the P+ emitter region 151 form an anode end portion of the thyristor. An N+ emitter region implant is carried out, such as shown in FIG. 1D, to complete the formation of the thyristor.

Thyristors formed in connection with the present invention can be implemented in a variety of manners, with selected examples discussed as follows. In one implementation, the P+ implant is effected using a relatively higher energy than used to effect the depth of the P+ region shown in FIG. 1E. In this implementation, the mask 124 is adapted to inhibit the P+ implant from implanting other portions of the substrate 102 while achieving a deeper implant through the portion 153 of the spacer layer. In another implementation, the doping of one or both of the N+ and P+ emitter regions is carried out concurrently with the formation of source/drain regions of other devices. In yet another implementation, the spacer 152 of FIG. 1E is formed as a symmetric spacer on both sides of the gate. In still another implementation, selected portions of the thyristor (e.g., the gate and the emitter regions) are salicided using the spacer 152 to block salicide formation over the N-base region 141 and to prevent the gate 118 and P+ emitter region 151 from shorting.

In another example embodiment of the present invention, the spacer and subsequent emitter region formation (using the spacer for self-alignment) is effected so that the spacer covers the junction between the base region over which the spacer is formed and the adjacent emitter region. This is particularly useful in processes with self-aligned silicide formation (salicide), so that salicide is prevented from shorting the junction between the second base region and the adjacent ernitter.

In the following figures, similar features described in connection with other figures are similarly labeled, and selected discussion of similar features, where repetitive, has been omitted. FIG. 2 shows a thin capacitively-coupled thyristor device 200, according to another example embodiment of the present invention. After a dopant for the N-base is implanted, a spacer 252 is formed over the gate 110 and having a portion 253 over the upper surface 104 of the substrate. A P+ implant is used to form a P+ emitter 250 having a generally consistent depth, resulting in a p-n junction 244 defining the width of the N-base region adjacent to the P+ emitter. After the P+ implantation is carried out, the spacer 124 can be removed and an N+ region (not shown) can be formed adjacent the P-base region 105, such as the N+ region 130 shown in FIG. 1D.

FIG. 3 shows a thin capacitively-coupled thyristor 300 formed according to another example embodiment of the present invention. Spacer 352 is formed having a portion 353 over the upper surface 104 of the substrate. The thickness of portion 353 is selected to prohibit P+ implantation through this portion, thereby resulting in a wider N-base 340 than would exist if the P+ implant would pass through the spacer and into the substrate below the spacer.

In a more particular example embodiment of the present invention, an optional etch stop layer 360 (shown having been partially removed) is formed over the gate 110 and upper portion 104 of the substrate. The etch stop layer may be formed using a material including a nitride and/or other materials that prevent etching. A spacer layer (shown having been etched) used to form spacer 352 is formed over the etch stop. A mask (not shown) is formed over the portion of the layer 352 shown in FIG. 3 and the layer is etched to form the spacer 352. The etch stop layer prevents other portions of the thyristor and/or other circuitry from being etched during the etching of the spacer layer. The portion of the etch stop layer not under the layer 352 is then etched, leaving the etch stop structure 360 as shown.

In another example implementation that can be understood with reference to the illustrated implementation of FIG. 3, the spacer 352 is etched to expose the etch stop layer 360. Salicide portions 370, 372 and 374 (shown with dashed lines) are then formed, respectively, over the exposed upper surface of the substrate 104 over the P+ region 350, N+ region 130 and over the gate polysilicon 118. The etch stop layer 360 and the spacer 112 prevent the salicidation from shorting between the gate salicide 374 and either of the salicide portions 370 and 372.

FIGS. 4A-4C show a thin capacitively-coupled thyristor device 400 being formed, according to another example embodiment of the present invention. In FIG. 4A, an etch stop layer 411 is formed over a poly gate 118 and a gate dielectric 116 and over a substrate 102 after doping of P-base and N-base regions (not shown) in the substrate. A spacer layer 413 is formed on the etch stop layer, a photoresist is patterned on the spacer layer (not shown) and the spacer layer is etched, resulting in the structure 413 shown in FIG. 4B.

As shown in FIG. 4C, the spacer layer 413 is then selectively anisotropically etched to form spacer 415, and the etch stop layer is selectively anisotropically etched to form spacers 412 and 414. The N+ cathode region 430 is doped using the spacer 412 to define a width of the P-base at p-n junction 434. The spacers 414 and 415 are then used to mask a portion of the N-base during implantation of a P+ anode region 450, resulting in the N-base 440 having a width defined by p-n junction 444 (between the N-base and the P+ emitter) and p-n junction 404 (between the n-base region 440 and the p-base region 405). In addition, and applicable to each of the embodiments herein, an offset between the corner of poly gate 118 and the closest junction is achieved by either: forming N-base region 440 after the region 414 has been formed; or by angle implantation after the spacer 415 is formed. This offset is useful in that it increases the forward breakover voltage of the thyristor which, in turn, improves the temperature stability, and it improves the ability to transition the thyristor from a current-passing to current-blocking state. After the P+ emitter region is formed, a salicidation is effected to form salicidc 470 over the N+ cathode 430, the poly gate 118 and the P+ anode 450, as shown. During the salicidation, the spacers 412 and 414 and the spacer 415 are used to prevent the formation of salicide over the N-base region 440 and over the p-n junctions 434 and 444 between the base and emitter regions of the thyristor.

FIGS. 5A-5D show a thin capacitively-coupled thyristor device 500 being manufactured, according to another example embodiment of the present invention. A P-base region 505 and an N-base region 540 (shown only in FIG. 5D for clarity) are formed in the substrate using, for example, methods such as those described above. In one implementation, the P-base region is formed during a P-well implant step, and the N-base region is formed during lightly doped drain (LDD) and/or S/D implants for other portions of the substrate. An etch stop layer 515 is formed over a poly gate 118 and a gate dielectric 116, spacers 112 and 114 and a substrate 102. A spacer layer 513 (e.g., oxide or other sufficiently-conformal material useful to form a spacer under-etch conditions) is formed over the etch stop layer, and is selectively anisotropically etched to form spacers 562 and 564, as shown in FIG. 5B.

In FIG. 5C, a photoresist 522 is patterned over a portion of the substrate, the spacer 562 and the etch stop layer 515. A P+ anode implant 552 is carried out using the spacer 564 to inhibit the P+ dopant below the spacer. After the P+ anode implant, the photoresist 522 and spacers 562 and 564 are removed, for example, using an isotropic etch with selectivity to etch stop layer 515.

FIG. 5D shows the resulting P+ anode emitter region 550 that defines a width of the N-base region 540 between p-n junction 544 and p-n junction 504. The etch stop layer 515 is masked and etched, leaving portions 517 and 519. A salicidation is then carried out to form salicide 570 over the N+ cathode 130, the poly gate 118 and the P+ anode emitter 550, as shown. The unetched etch stop regions 517 and 519 act as a salicide block.

FIGS. 6A-6C show a thin capacitively-coupled thyristor 600 being manufactured, according to another example embodiment of the present invention. In FIG. 6A, a thin etch stop layer 615 is formed over a poly gate 118, a gate dielectric 116 and a substrate 102. A spacer layer 660 is formed on the etch stop layer 615. In FIG. 6B, the spacer layer is selectively anisotropically etched, leaving portions 662 and 664. A mask 620, such as a photoresist, is then patterned as shown, and the spacer portion 662 is removed using, for example, an isotropic etch with high selectivity to the underlying etch stop layer 615.

In FIG. 6C, spacer portion 662 is removed and a second spacer layer is deposited and etched back to form spacers 674 and 673. The etch stop layer 615 is also etched back, leaving etch stops 613 and 614 adjacent to the thyristor gate sidewalls. An N+ cathode emitter region 130 is implanted using the spacer 673 to inhibit the N+ implant below the spacer. In addition, using the previously-discussed angled implant approach, a P+ anode emitter region 650 is implanted using the remaining portion 614 of the etch stop and the spacers 664 and 674 to inhibit the implant, and the N-base region 640 is formed having a width defined at p-n junction 644 between the N-base and the implanted P+ emitter regions. After the emitter regions are formed, salicide 670 is formed on the N+ emitter region 130, P+ emitter region 650 and poly gate region 118.

FIGS. 7A-7B show a thin capacitively-coupled thyristor 700 being manufactured as an alternative approach to that shown in connection with FIG. 1E. In FIG. 7A, a control port stack including a control port 718 on a dielectric 716 and having sidewalls 712 and 714 is formed over a p-doped substrate 705 in a substrate region 702. A photoresist layer 732 is formed over the control port 718, spacer 714 and P-doped substrate 705. Using the photoresist layer 732 as a mask, N+ emitter region 730 is implanted in the substrate region 702 and aligned to the control port 718 and spacer 712.

In FIG. 7B, the photoresist material 732 has been removed and a salicide block layer 752 is formed on the control port 718, spacer 714 and substrate region 702. A photoresist layer 734 is formed over the salicide block layer 752, the control port 718, spacer 712 and N+ emitter region 730. An angled N-base implant is carried out to form N-base region 740 (at this later stage of the manufacturing process), and a P+ anode implant is carried out to form P+ emitter region 750, both using the salicide block as a mask.

As an alternative approach, any of the above embodiments can be modified using the approach(es) illustrated and described in concurrently-filed U.S. Provisional Patent Application Serial No. 60/415,368 (TRAM.036P1), entitled “Implant Approach With Self-Alignment to Salicide Block.”

The various embodiments described above are provided by way of illustration only and should not be construed to limit the invention. Based on the above discussion and illustrations, those skilled in the art will readily recognize that various modifications and changes may be made to the present invention without strictly following the exemplary embodiments and applications illustrated and described herein. Such changes may include, but are not necessarily limited to: altering the shapes, locations, and sizes of the illustrated thyristors; adding structures to the integrated circuit device; increasing the number of p-n sections in the thyristor-based memory device; and interchanging P and N regions in the device structures and/or using PMOSFETS or NMOSFETS in connection with the thyristors. In addition, it will be appreciated that use of the term “MOS” generally encompasses other FET-type semiconductor devices (IGFETs), for example, where oxide is not necessarily used. For more information regarding implementations to which the present invention is applicable and their respective operations and detailed construction, reference may be made to U.S. Pat. No. 6,229,161, which is fully incorporated herein by reference. Such modifications and changes do not depart from the true spirit and scope of the present invention that is set forth in the following claims. 

What is claimed is:
 1. A method for forming a thyristor-based memory device, the method comprising: providing a semiconductor substrate having an upper surface and a doped portion therein; forming a thyristor gate over a first region of the doped substrate; using the gate to mask the first region; doping a second region of the substrate; forming a spacer adjacent to the gate and over the second region; and using the spacer to mask the second region, doping a third region of the substrate, the first and third regions being contiguously adjacent to the second region, the thyristor including doped regions of which the first and second regions are base regions and the third region is a first emitter region.
 2. The method of claim 1, wherein one of the first and second regions is doped with a P type dopant; wherein the other one of the first and second regions is doped with an N type dopant; and wherein the step of doping a second region occurs: before forming a spacer, or after the step of forming a spacer.
 3. The method of claim 1, further comprising using the spacer to block salicide formation over a junction between the second and third regions.
 4. The method of claim 1, further comprising using the gate to mask the first region and doping a region of the substrate to form a second emitter region of the thyristor that is contiguously adjacent the first region.
 5. The method of claim 4, wherein forming the spacer includes forming a sidewall spacer on the gate, prior to doping the second emitter region contiguously adjacent the first region, wherein the sidewall spacer inhibits the doping of the substrate below the sidewall spacer.
 6. The method of claim 1, further comprising forming a mask over a portion of the substrate that is adjacent to the thyristor gate and on an opposite side of the gate from the spacer, prior to doping the third region, the mask being adapted to inhibit implantation of the substrate below the mask.
 7. The method of claim 1, wherein doping the third region of the substrate includes using a high energy implant that is adapted to penetrate a layer of material over the substrate.
 8. The method of claim 7, wherein forming the spacer over the second region includes forming a spacer layer over the gate and wherein using the high energy implant includes using the spacer layer over the gate to inhibit implantation through the gate.
 9. The method of claim 7, wherein forming the spacer includes forming at least one sidewall spacer adjacent to a sidewall of the thyristor gate, prior to doping the second and third regions, further comprising forming a second spacer over the sidewall spacer and over a portion of the substrate adjacent to the sidewall spacer, wherein using the spacer to mask the second region includes using the sidewall spacer and the second spacer as a mask, wherein the high energy implant is sufficient to penetrate a portion of the second spacer that is over the substrate adjacent to the sidewall spacer.
 10. The method of claim 9, wherein forming at least one sidewall spacer includes forming spacers on two sidewalls of the thyristor gate.
 11. The method of claim 10, wherein forming spacers on two sidewalls of the thyristor gate includes forming two symmetric spacers.
 12. The method of claim 1, further comprising masking and etching the spacer, prior to using the spacer as a mask.
 13. The method of claim 12, wherein masking and etching the spacer includes exposing a portion of the upper surface and wherein doping the third region includes doping a portion of the third region below the spacer to a depth into the substrate that is less than the depth of another portion of the third region doped via the exposed upper surface.
 14. The method of claim 1, wherein the third region is doped concurrently with the doping of a source/drain region of a transistor in a semiconductor device in which the thyristor is being formed.
 15. The method of claim 1, wherein forming the spacer includes forming at least one of: nitride and oxide.
 16. The method of claim 1, wherein forming the spacer over the second region includes forming a spacer layer that is sufficiently thick to block the third region from being doped below the spacer layer.
 17. The method of claim 1, further comprising forming an etch stop over the second region, prior to forming the spacer over the second region, further comprising using the etch stop to prevent the etching of the second region during subsequent etching of the spacer.
 18. The method of claim 1, further comprising forming an etch stop layer over the second region, prior to forming the spacer over the second region and wherein using the spacer to mask the second region includes using the etch stop layer to mask the second region.
 19. The method of claim 18, further comprising selectively anisotropically etching the spacer and the etch stop layer and forming a spacer on a sidewall of the gate that includes the etched spacer and the etch stop layer, prior to doping the third region and wherein using the spacer and the etch stop layer to mask the second region includes using the sidewall spacer to mask the second region.
 20. The method of claim 1, wherein forming the spacer comprises: forming a sidewall spacer on a sidewall of the gate and over the second region; forming a thin etch stop over the gate, the sidewall spacer and a portion of the substrate adjacent to the sidewall spacer; forming a second spacer layer over the thin etch stop; selectively anisotropically etching the second spacer layer and forming a second spacer over the second region, wherein using the spacer to mask the second region includes using the sidewall spacer, the thin etch stop and the second spacer to mask the second region; after doping the third region of the substrate, removing the second spacer and a portion of the etch stop; and using the sidewall spacer and the remaining portion of the etch stop as a salicide block, forming a salicide over the gate and the third region.
 21. The method of claim 1, wherein forming the spacer comprises: forming an etch stop layer over the gate and the substrate; forming a spacer layer over the etch stop; selectively anisotropically etching the spacer layer and forming spacers contiguously adjacent a portion of the etch stop that is on sidewalls of the gate; masking one of the spacers; etching and removing the unmasked spacer; removing the mask; forming a second spacer in place of the removed spacer and a second spacer over the first spacer, wherein using the spacer to mask the second region includes using a portion of the etch stop, the first spacer, and the second spacer to mask the second region; and further comprising using the second spacer and the etch stop to mask a portion of the substrate and doping a fourth region of the substrate to form a second emitter region of the thyristor.
 22. The method of claim 1, wherein doping a second region of the substrate includes doping the second region of the substrate prior to forming the spacer.
 23. The method of claim 1, wherein doping a second region of the substrate includes doping the second region of the substrate after forming the spacer.
 24. A method for forming a thin capacitively coupled thyristor, the method comprising: doping a portion of a substrate having an upper surface with a first dopant and forming a first base region of the thin capacitively-coupled thyristor; forming a gate stack over the first base region, the gate stack including a gate dielectric on the upper surface and a polysilicon gate electrode over the gate dielectric; using the gate stack as a mask and doping a portion of the substrate adjacent to the gate stack with a second dopant and forming a second base region contiguously adjacent the first base region; forming a spacer layer over at least a portion of the gate stack, the second base region and the substrate surface adjacent the second base region; using the spacer layer to mask a portion of the second base region, doping a portion of the substrate adjacent to the second base region with a third dopant and forming an emitter region of the thyristor that is self-aligned to the spacer; using the gate stack as a mask and doping a portion of the substrate adjacent to the gate stack with a fourth dopant and forming an emitter region contiguously adjacent the first base region; and forming a salicide over a portion of the thyristor while using the spacer to block salicide formation over another portion of the thyristor.
 25. A method for forming a semiconductor device including a thyristor, the method comprising: providing a semiconductor substrate having an upper surface and a doped portion therein; forming a thyristor control port over a first region of the doped substrate and then doping a second region of the substrate, the second region being laterally offset from the control port; and forming a spacer adjacent to the control port and over the second region and then doping a third region of the substrate, the first and third regions being contiguously adjacent to the second region, the thyristor including doped regions of which the first and second regions are base regions and the third region is a first emitter region.
 26. The method of claim 25, wherein doping a second region of the substrate includes using the control port to mask the first region.
 27. The method of claim 25, wherein doping a third region of the substrate includes using the spacer to mask the second region.
 28. The method of claim 25, wherein doping a second region of the substrate includes using an angled implant.
 29. The method of claim 25, wherein doping a second region of the substrate includes forming a spacer immediately laterally adjacent to the control port and using the spacer to laterally offset the second region from the control port.
 30. The method of claim 29, wherein forming a spacer immediately laterally adjacent to the gate includes forming spacing material laterally adjacent to a first side of the control port and over the first region and wherein doping a second region of the substrate includes using the control port and spacing material to mask a contiguous portion of the first region under the control port and under the spacing material.
 31. The method of claim 30, further comprising forming a second emitter region coupled to the first base region, the emitter and base regions forming a thyristor body, wherein the control port and the thyristor body are arranged such that the control port is adapted for capacitively coupling to the first base region.
 32. The method of claim 25, wherein doping a second base region in the substrate includes forming a p-n junction that defines an interface between the first and second base regions, the control port not extending over the interface.
 33. The method of claim 25, wherein doping a second region of the substrate includes at least one of: using an angled implant to laterally offset the second region from the gate; and forming a spacer immediately laterally adjacent to the gate and using the spacer to laterally offset the second region from the gate. 